1. Field of the Invention
The present invention relates to a fuel gas production apparatus for reforming a hydrogen-containing fuel into a reformed gas, and refining the reformed gas to produce a hydrogen-rich fuel gas. Further, the present invention relates to a method of starting operation of the fuel gas production apparatus.
2. Description of the Related Art
For example, hydrogen production apparatuses (fuel gas production apparatuses) for reforming a hydrocarbon fuel such as natural gas or a hydrogen-containing fuel such as an alcohol (e.g., methanol) into a hydrogen-containing gas (reformed gas), and refining the hydrogen-containing gas to produce a fuel gas supplied to a fuel cell or the like are adopted conventionally.
For example, Japanese Laid-Open Patent Publication No. 2002-20102 discloses a hydrogen production apparatus shown in FIG. 21. The hydrogen production apparatus includes a compressor 1, a hydrodesulfurization unit 2, a steam reformer 3, a catalyst combustor 4, a gas shift reactor 5, and a PSA (Pressure Swing Adsorption) unit 6. A fuel gas such as a city gas is supplied to the hydrodesulfurization unit 2. After desulfurization of the fuel, the steam reformer 3 reforms the fuel by steam reforming to produce a hydrogen-containing gas (hydrogen rich gas). The catalyst combustor 4 is provided around the steam reformer 3, and combusts the hydrogen and oxygen in the air using catalyst. The gas shift reactor 5 induces a shift reaction for converting carbon monoxide in the hydrogen-containing gas into carbon dioxide and hydrogen. After the gas shift reaction, the PSA unit 6 refines the hydrogen-containing gas into highly pure hydrogen by pressure adsorption.
A hydrogen storage tank 8 and an off gas holder 9 are connected to the PSA unit 6. The hydrogen storage tank 8 temporarily stores the highly pure hydrogen before it is supplied to a polymer electrolyte fuel cell (PEFC) 7. The off gas holder 9 temporarily stores the off gas (impurities) removed by pressure adsorption in the PSA unit 6. The off gas holder 9 supplies the off gas to the catalyst combustor 4 as a fuel for heating the steam reformer 3.
The PSA unit 6 has a plurality of adsorption towers filled with adsorbent material for selectively adsorbing impurities (components other than hydrogen) under high pressure, and desorbing the adsorbed components under low pressure. A series of steps comprising adsorption of impurities, desorption of impurities, replacement of the gas, and pressurization are performed in a cyclic manner in each of the adsorption towers for obtaining the highly pure hydrogen, and discharging the other gas components as the off gas.
For the purpose of interrupting operation of the hydrogen production apparatus, the PSA unit 6 stores interruption conditions of the respective towers in advance. Assuming that the PSA unit 6 has three adsorption towers, generally, two adsorption towers are stopped at high pressures, and the remaining one tower is stopped at a pressure substantially the same as, or lower than the air pressure. The pressure condition is maintained until operation of the hydrogen production apparatus is started again.
However, if operation of the hydrogen production apparatus is suspended for a long period of time, transition to the chemical equilibrium condition occurs in the towers at the high pressure, and the gas components tend to be distributed uniformly in the towers. Thus, when operation of the hydrogen production apparatus is started from the cleaning step, gas components of the cleaning gas moving between the towers may include a lot of impurity components such as a carbon dioxide gas or a nitrogen gas, though the chief gas component of the intended cleaning gas is the hydrogen gas. The impurity gas has a large pipe resistance in comparison with the hydrogen gas.
Therefore, the flow rate of the cleaning gas is reduced, and the amount of the discharged off gas is reduced. As a result, calorie shortage occurs for the capacity of the catalyst combustor 4, and the temperature of the catalyst combustor 4 decreases. In order to address the problem, it is necessary to provide additional fuel supply to the catalyst combustor 4.
Further, in the desorption step, a large amount of the off gas remaining in the towers is supplied to the catalyst combustor 4. Therefore, the catalyst combustor 4 may be heated to the excessively high temperature. Thus, thermal load is applied to the catalyst combustor 4 undesirably.